The invention relates to a fibre-resin composite body for providing electromagnetic shielding, at least comprising an electrically conductive fibre fabric, partially or wholly embedded in the fibre-resin material.
The electrically conductive layer in a body of this type creates the possibility to provide electromagnetic shielding notwithstanding the fact that low-conductive composite materials are utilized. The body may, for instance, be implemented as a cover plate or protective hood. If the body in question is implemented as a protective hood, it is suitable for shielding parts susceptible to electromagnetic radiation or parts emitting undesirable electromagnetic radiation in, for instance, a radar apparatus. In certain types of radar apparatus it is required to provide adequate electromagnetic shielding within overlap areas between the protecting hood and adjacent units. If prior art protective hoods are applied, this shielding does not provide a sufficient degree of shielding, since electromagnetic radiation may leak out through the lap joint.
The body according to the invention aims at enhancing the prior art body and is thereto characterized in that one surface of the body has an insulated and an uninsulated area, the latter area being wholly or partially covered with an electrically conductive contact strip which provides a direct electrical connection with the conductive fibre fabric. Thus, direct electrical contact can be established between the protective covering and adjacent units, resulting in a local strong electromagnetic shielding.
An advantageous embodiment is characterized in that the conductive strip comprises a wire mesh. This entails the advantage that lamination of the strip can be included in the overall lamination process.
The invention additionally relates to a method for fabricating a fibre-resin composite body for providing electromagnetic shielding, at least comprising an electrically conductive fibre fabric, wholly or partially embedded in the fibre-resin material, said body comprising on one surface thereof an insulated area and an uninsulated area, the latter area being wholly or partially covered with an electrically conductive contact strip which provides a direct electrical connection with the conductive fibre fabric, said method comprising the steps of:
placing the fibre fabric with the non-cured resin in the mould;
placing the conductive contact strip on the electrically conductive fibre fabric;
covering the electrically conductive contact strip or a part thereof with a sealing tape;
subsequent curing of the resin;
removing the sealing tape after the cure cycle has at least substantially expired.
In actual practice, the construction of a fibre-resin composite protective hood or plate comprising a conductive layer and a contact strip for providing direct electrical connection with the conductive layer, has proven to be quite complex. In this context, an obvious fabrication method would be to remove resin caused by lamination from the area that is to accommodate the contact strip and to apply the contact strip after lamination. The advantage of the method according to the invention is, however, that lamination of the contact strip is included in the overall lamination process, which obviates the need for the above-described operations.
By preference, the method is effected such that during the cure cycle, an external pressure force is exerted on the body such that a compact structure is obtained. Preferably prior to curing, the body to be moulded is hermetically sealed by means of a foil after which the space that contains the body to be moulded, is at least substantially evacuated, resulting in an even distribution of pressure on the body.
The conductive fibre fabric is by preference laminated along with a resin-impregnated fibre fabric, a so-called prepreg which is commercially available. During the curing process under a vacuum, the non-cured resin is also found to infiltrate the conductive fibre fabric.
If the contact strip comprises a wire mesh, a good electrical contact with the conductive layer is ensured during lamination. The vacuum process will cause the mesh to be pressed firmly against the electrically conductive layer, while the non-cured resin will be pressed between the filaments of the mesh, so that the mesh is bonded to the conductive layer. The sealing foil or tape is pressed firmly against the side of the contact strip that is to remain uninsulated so as to prevent resin inclusion during the curing cycle.
If the sealing tape is made of a silicone-based material, it can be easily removed after the lamination process.
The above-described process can take place during a low-temperature curing cycle.